1. Technical Field
The present invention relates to measuring tools and, particularly, to an apparatus for measuring a thickness of a lens.
2. Description of Related Art
With the development of optical imaging technology, camera devices, such as digital cameras and mobile phones, are widely used in electronic devices. Optical lenses are one of the most critical components in any camera device.
Typically, optical lenses are made by an injection molding process. After the injection molding process, a thickness of the lens needs to be measured by an apparatus (see “A Novel Optical Method of Dimension Measurement of Objects with Circular Cross-section”, Instrumentation and Measurement Technology Conference, 2006).
Referring to FIG. 6, a surface profile meter 50 used for measuring a thickness of a lens 52 is illustrated. The surface profile meter 50 includes a probe 502. The lens 52 has two surfaces 522 and 524 facing away from each other. The thickness of the lens 52 is usually taken as the greatest distance between generally central peak points of each of the two surfaces 522 and 524. The probe 502 is driven to touch and slide on the surface 522 until the peak point of the surface 522 is detected by the surface profile meter 50 and the same is done for the other surface 524. Unfortunately, the surface profile meter 50 is very expensive, and may give inaccurate results if orientation of the lens is not correct or bending of the lens occurs.
Referring to FIG. 7, a height gauge 60 for measuring the thickness of the lens 52 is illustrated in accordance with a conventional technology. The height gauge 60 includes a touch head 602 and a base 604. In use, the lens 52 is disposed on the base 604 with the surface 524 touching a surface of the base 604. Then, one end of the touch head 602 touches the surface 522. A distance between the end of the touch head 602 and the surface of the base 604 is a thickness of the lens 52.
The height gauge 60 is much cheaper than the surface profile meter 50. However, the surface of the base 604 and the end face of the touch head 602 are both plane, which may result in tilting of an optical axis of the lens 52 with respect to a vertical line of the surface of the base 604, and thus errors may occur. Besides, contact faces between the surface 522 and the end face of the touch head 602 and between the surface 524 and the surface of the base 604 are small, which may result in the lens 52 distorting, and thus decreasing the measuring precision of the lens 52.
What is needed, therefore, is an apparatus for measuring a thickness of a lens with higher precision.